As an exhaust pipe introducing an exhaust gas to the vehicle body rear part from an engine for an automobile through a manifold, a double-layer metal pipe provided with a minute gap (10-150 μm) between an outer tube and an inner tube is proposed in the Patent literature 1 and the like.
The object of the double-layer metal pipe is to improve the noise reduction performance by damping vibration of the inner tube generated by vibration of the engine and pulsation of the exhaust gas pressure by the minute gap.